The popular media promote a plethora of energy-reduction ideas for consumers and precious few for industry. Since industry consumes 33% of the natural gas, 25% of the renewable energy, 23% of the petroleum and 8% of the coal produced in the U.S. (2011 statistics), this absence might appear to be a major lapse in editorial judgment by the pop-culture pundits.
The popular media promote a
plethora of energy-reduction ideas for consumers (light bulbs, thermostats,
screen savers, weather stripping, etc.) and precious few for industry. Since
industry consumes 33% of the natural gas, 25% of the renewable energy, 23% of
the petroleum and 8% of the coal produced in the U.S. (2011 statistics), this
absence might appear to be a major lapse in editorial judgment by the
contrary, energy reduction in the industrial sector, while rich with
money-saving potential, usually involves a higher level of nuance and narrower
applicability than the common denominators typically understood by mass media
and the public. In industry, the bulk of energy goes into processes – many of
which are chemically and mechanically complex and involve safeguards that must
not be disregarded. Below are some examples of how higher levels of risk may
accompany energy-saving process changes.
Adding a recuperative or
regenerative heat exchanger to a combustion process can save energy by
preheating the combustion air and simultaneously reducing the temperature of wasted
exhaust gases. However, there are risks associated with these process changes
in some systems, including burner instabilities due to excessive turndown or
disproportionately high temperatures if firing rate can’t be turned down
Flue-gas recirculation (FGR) and oxygen-enriched combustion are two
contrasting methods for reducing waste of hot gas exhausted to atmosphere.
Oxygen-enriched combustion reduces the nitrogen content in the exhaust stream
and thereby eliminates the waste of a significant portion of the hot gas
stream. In order to transfer the same amount of heat to the load, however, the
resulting higher flame temperatures are capable of damaging the burner or
furnace. Conversely, FGR is capable of delivering the same amount of heat to a
load with reduced exhaust-gas waste and without excessive flame temperatures.
Unfortunately, FGR reduces oxygen in the furnace and may cause flame
instabilities, nuisance shutdowns or worse.
Reducing furnace exterior temperatures by installing
better insulation can cut heat losses, which saves fuel year-round and reduces
worker discomfort in summer. Under some operating conditions (e.g.,
oxygen-deficient atmosphere), however, dropping the exterior wall temperature
below a critical point can cause hydrocarbons to diffuse and deposit into
porous insulating materials and create subsequent problems such as fire or
environmental contamination. Alternatively, if acid gases are present in the
furnace, these may diffuse through insulating materials and condense on a cold
wall, causing corrosion and deterioration of the furnace shell.
High-temperature thermal storage is becoming more
commonplace, and molten salt is proving to be a popular storage medium. For
metallurgical operations with molten-salt quench baths, a solar concentrating
system can be employed to heat and melt the salt, which can then be stored
overnight in a well-insulated vessel. However, solar mirrors are not
hazard-free devices. Mirrors that focus sunlight can cause skin or eye injuries
if they malfunction when workers are in vulnerable locations.
Replacement of traditional
fossil fuels with biofuels or waste-to-energy fuel blends may save money and
reduce carbon emissions, but burners and other combustion-system components
likely need replacement or redesign to safely burn non-traditional fuels.
Secondary consequences (e.g., plugging, fouling) related to ash or slag
accumulation may also result from the combustion of bio-solids. Storage and
handling of combustible solids may lead to unintended accumulations of
combustible dust and the explosion hazards associated therewith.
The bottom line: When
implementing a new energy-saving idea, seek assistance from a trusted member of
the technical staff or outside specialist if the changes could affect process
safety. Perform appropriate safety reviews and obtain engineering change
approvals if system functionality will be altered in any significant way.IH
This month’s column is my last
as a regular contributor to Industrial Heating magazine. I
have been writing about safety and environmental issues in this space since
January 2008, and it has been a pleasure to have researched and opined on a
wide variety of interesting and practical topics. I want express my gratitude
to IH and BNP for providing me the opportunity to do something I love – write
about thermal technologies. And to IH readers, I send a strong wish for your
workplaces to be enriched with excellence as you practice safety for your
colleagues and care for the environment.
Energy vs. Safety - Trade-offs and Risks
July 9, 2012